Abstract： Objective To evaluate different shunting flow in varied conditions in a simulated adult cardiopulmonary bypass (CPB) model under normothermia. Methods We established the pseudo adult patient undergoing CPB at four different shunting states with devices of heartlung machine, heatcooler, an adult membrane oxygenator and arterial filter. In state 1, purge line of the arterial filter was open alone; In state 2, purge line combined with 6.5 mm tubing hemoconcentrator shunting was open; In state 3, purge line combined with 5 mm tubing hemoconcentrator was open; In state 4, purge line combined with blood cardioplegia shunting was open. The flow of preoxygenator and postfilter was recorded with ultrasonic flowmeter, and the pressure of purge line and postarterial filter was also detected. Results At state 1, when the pump flow was invariable, the percentage of the shunting flow increased with the increase of postfilter pressure. However, when the postfilter pressure was constant, the percentage of the shunting flow decreased with the increase of the pump flow. The purge line pressure increased with the increase of the postfilter pressure at a constant pump flow under state 1. The shunting flow of state 2 was the largest among all the four states. The shunting flow of state 3 was similar to that of state 4. All the purge line pressure was lower than the postfiler pressure of the circuit in the four states. Conclusion Under states of different shunting opening, different degrees of blood flow are diverted away from the arterial line. The shunting flow increases at a lower pump flow and a higher postfilter pressure. A flow probe located in the postfilter line may be necessary to monitor realtime arterial flow.